Potential Gradient‐Driven Dual‐Functional Electrochromic and Electrochemical Device Based on a Shared Electrode Design

Abstract The integration of electrochromic devices and energy storage systems in wearable electronics is highly desirable yet challenging, because self‐powered electrochromic devices often require an open system design for continuous replenishment of the strong oxidants to enable the coloring/bleaching processes. A self‐powered electrochromic device has been developed with a close configuration by integrating a Zn/MnO2 ionic battery into the Prussian blue (PB)‐based electrochromic system. Zn and MnO2 electrodes, as dual shared electrodes, the former one can reduce the PB electrode to the Prussian white (PW) electrode and serves as the anode in the battery; the latter electrode can oxidize the PW electrode to its initial state and acts as the cathode in the battery. The bleaching/coloring processes are driven by the gradient potential between Zn/PB and PW/MnO2 electrodes. The as‐prepared Zn||PB||MnO2 system demonstrates superior electrochromic performance, including excellent optical contrast (80.6%), fast self‐bleaching/coloring speed (2.0/3.2 s for bleaching/coloring), and long‐term self‐powered electrochromic cycles. An air‐working Zn||PB||MnO2 device is also developed with a 70.3% optical contrast, fast switching speed (2.2/4.8 s for bleaching/coloring), and over 80 self‐bleaching/coloring cycles. Furthermore, the closed nature enables the fabrication of various flexible electrochromic devices, exhibiting great potentials for the next‐generation wearable electrochromic devices.

Comparison of the optical contrast and switching speed of our Zn||PB||MnO2 system with recently reported electrochromic systems.Note: "Half" means that these electrochromic systems can only achieve a unidirectional coloring or bleaching transition, while still need to be connected to an external power supply to revert to their initial states.
When connecting the PB electrode to Zn in the Zn||PB||MnO2 system, electrons flow from the Zn electrode to the PB electrode, reducing Fe 3+ to Fe 2+ and leading to the transformation of the blue PB electrode to the colorless PW electrode.After the PW electrode is switched to connect with MnO2 electrode, electrons flow from PW electrode to MnO2 electrode and lead to blue PB.Both the bleaching and coloring processes are driven by the potential difference between Zn/PB electrodes and PW/MnO2 electrodes.Movie S2-S4 demonstrate the self-powered bleaching and coloring switching of the wearable electrochromic glasses, labels, and wristband, respectively.Movie S5 demonstrates the electrochromic performance of the real air-working Zn||PB||MnO2 electrochromic system.Movie S6 shows the electrochromic label in flat and folded states.
Figure S1.a) TEM image, b-c) elemental mapping images, d-e) HR-TEM images, and f) SAED pattern of MnO2.
Figure S1.a) TEM image, b-c) elemental mapping images, d-e) HR-TEM images, and f) SAED pattern of MnO2.

Figure S2 .
Figure S2.UV-vis spectra of PB electrodes with electrochemical deposition times of 300s, 600s, and 900s at -15μA cm -2 electrodeposition current density, the transmittance of the FTO glass or ITO/PET was used as the baseline during the measurement.

Figure S3 .
Figure S3.EDS mapping of the PB electrode and the compositional distributions of K, Fe, C and N elements.

Figure S4 .
Figure S4.a) XRD patterns of FTO, PB-FTO, ITO/PET, and PB-ITO/PET, b) TEM image, c) elemental mapping images, d-e) HR-TEM images and f) SAED pattern of PB powder.The PB samples are scraped from the PB-FTO glass.

Figure S5 .
Figure S5.In situ potential measurement of the PB electrode when it connects to Zn electrode and ECP electrode in turn.When the PB electrode connects to the Zn electrode, the potential rapidly decreases as electrons flow from the Zn electrode to the PB electrode, resulting in the reduction of Fe 3+ to Fe 2+ and the transformation of the blue PB electrode into the colorless PW electrode.Upon connecting the PW electrode to the MnO2 electrode, electrons flow from the PW electrode to the MnO2 electrode, causing an increase in the potential.Following disconnection from the MnO2 electrode, the potential returns to its initial state.

Figure S7 .
Figure S7.a) The switching speed of the 1 th and 2 nd electrochromic cycle; b) The synchronized transmittance profile and the overall cell potential; c) The switching speed of the 101 th and 102 nd electrochromic cycle, the switching times are set to 10 s.

Figure S8 .
Figure S8.a) The SEM image and the corresponding EDS mapping of the post-electrochromic (discharged) MnO2 electrode, revealing a significant presence of Zn and K elements, and after charging, most Zn elements and all K elements disappeared.

Figure
Figure S9.a) In situ transmittance measurement of the Zn||PB||MnO2 electrochromic system in the electrolyte with/without K + ; b) CV curves of the PB film in the electrolyte with and without K + .

Figure S10 .
Figure S10.Electrochromic performance of the real air-working Zn||PB||MnO2 electrochromic system.a) and b) Optical photos of bleached state and colored state of PB electrode; c) UV-vis transparence spectra of PB and PW; d) In situ transmittance measurement at 700nm of PB connected with Zn electrode and MnO2 electrode for 10 s, respectively; e) In situ transmittance measurement of Zn||PB||MnO2 system under repeated bleaching and coloring cycles, the switching time is set to 10 s.

Figure S11 .
Figure S11.In situ transmittance measurement of Zn||PB||MnO2 system under repeated bleaching and coloring cycles after repeating charging and electrochromic-discharging for 50 times, the switching time is set to 10s.

Figure
Figure S12.a) Cyclic voltammetry curve of MnO2 cathode at a scan rate of 1 mV s -1 ; b) The rate capability and c) Charge-discharge profiles of the Zn/MnO2 battery; Cyclic performance of Zn/MnO2 battery at d) 0.1 A g -1 and e) 1 A g -1 .

Figure S14 .
Figure S14.Preparation of the electrochromic label utilizing galvanic-driven deposition method.Briefly, A piece of metallic nickel was tightly attached to the conductive side of the ITO/PET substrate through a conductive double-sided tape, and then immersed into a

Figure S16 .
Figure S16.The electrochromic label operates at ice/hot water, a-b) Bleached and colored states at ~6℃; c-d) Bleached and colored states at ~44℃; The electrochromic label in e) flat and f) folded states.